1. Field of the Invention
The present invention relates to a process for preparing a polyurethane prepolymer, which comprises addition reacting acid anhydride derivative with triol or tetraol compound to give a diol or triol monomer which has carboxylic acid moiety or both carboxylic acid moiety and a double bond, and reacting polyol with diisocyanate by the use of the diol or triol monomer to prepare polyurethane prepolymer; and a process for preparing a water-stable aqueous polyurethane dispersion by neutralizing the polyurethane prepolymer obtained as above, dispersing it in water, and performing a chain extension.
Further, the present invention relates to a use of the aqueous polyurethane dispersion for a coating agent, an adhesive agent, a fiber treating agent, a paper processing agent, a leather treating agent, an adhesive for plywood, a blending agent for cement, a resin for synthetic leathers, or the like.
2. Prior Arts
A variety of processes for preparing aqueous polyurethane dispersions have been known. The dispersions are largely divided into two groups of ionic type and nonionic type, depending on the existence or non-existence of ion in the chain. Ionic type dispersions are divided into anionic type and cationic type.
In case of anionic type, sulfonate type and carboxylate type dispersions are widely used, while in case of cationic type, quaternary amine type dispersions are widely used. The most general type among these is anionic type including a carboxylic acid moiety.
In other words, a water-dispersible polyurethane is obtained by admixing dimethylolpropionic acid (DMPA) having carboxylic acid with the polyol or diisocyanate to perform an addition reaction to give a prepolymer whose end is terminated by NCO; neutralizing and dispersing the prepolymer in water by self-emulsification; and performing a chain extension reaction. In the process, a variety of methods have been disclosed on the introduction of a hydrophilic group (for example, --COOH group) which is able to be self-emulsified.
For instance, according to the disclosure of U.S. Pat. No. 4,250,077 (issued to von Bonin et al.), an unsaturated carboxylic acid having double bond(s) was mixed with various type of polyols, and the mixture was homopolymerized with a free radical initiator to obtain a graft polymer. In other words, a carboxylic group is introduced by graft polymerization to the main chain. In the patent, the precise mechanism of the polymerization is not shown.
U.S. Pat. No. 4,460,738 (issued to Frentzel et al.) discloses a process where a carboxylic group is introduced by a free radical addition reaction on a main chain of polyether polyol, which is an oxyalkylene adduct. By using tripropyleneglycol as a polyether polyol, and maleic acid, fumaric acid, or itaconic acid as a monomer having carboxylic group(s), and by introducing a peroxide-type free radical initiator thereinto, a polyether polyol having carboxylic acid was prepared in a radical addition reaction.